STRUCTUKE OF THE OVUM IN THE INVERTEBRATA. 187 



Our information is most incomplete in regard to the female 

 organ of the Rhizopoda. The few statements made by the 

 above-named authors lead us to suppose that the structure 

 that here contains the eggs is similar to the nucleus of the 

 Infusoria. 



The C^LENTERATA everywhere exhibit special organs for the 

 production of the ova, which in the higher orders, as in the 

 Actinia, Ctenophora, etc., have a follicular form. The ova are 

 believed to originate from the cells lining the follicles. As a 

 general rule the capsules of the ova appear as appendages of 

 the gastro-vascular apparatus, and in many instances as pro- 

 trusions of the latter ; for, as is well known, in these animals the 

 generative products are discharged into the gastric cavity, or 

 into the canals that radiate 'from it. 



The ovaries of the ECHINODERMATA are composed of rounded 

 or elongated tubes that are usually united together into 

 several gland-like groups, corresponding in their number and 

 arrangement with the radial segments of the body. In the 

 higher forms, as, for example, in the Holothuriadse (see Selenka, 

 105), the small gland tubes open into one or more excretory 

 ducts. The ova lie closely compressed in the gland tubes; their 

 mode of development, however, still requires investigation. 

 When mature, they possess a thick vitelline membrane, that 

 exhibits a radial striation and an aperture that is to be 

 regarded as a micropyle (see page 177). 



As regards the ovaries of VERMES, I may refer to the investi- 

 gations of Meissner (75), Bischoff (134), Munk (81), Leuckart 

 (67), Hering (51), Claparede (27, 28), and others, as well as to 

 my own researches on the Ascaridse, from which the following 

 conclusions may be drawn. The true ovary is either a vesicular 

 organ opening by a special excretory duct into the compli- 

 cated sexual canal, or, as in the Ascaridse, it consitutes the 

 ultimate csecal extremity of the genital tube. But since in 

 many Yermes, and especially in the parasitic forms, such as the 

 Cestodes and Trematodes, special glands are also present, which, 

 since the time of Siebold, have been termed yolk-stocks (" vitel- 

 ligene," " dotterstocke "), we must here distinguish the ovary 

 proper by the term " germ-stock " (" germigene," " keimstock "). 

 As regards the function of these two glandular organs, which 



